1. Field of the Invention
The present invention relates to an apparatus and method useful for obtaining improved dental castings according to the lost wax method. The apparatus and method of this invention permit dental castings of extreme accuracy to be prepared using base metal alloys rather than precious metals such as gold and the like.
2. Description of the Prior Art
Various techniques and forms of apparatus are old and well known for preparing castings according to the lost wax method. Use of the lost wax method within the dental profession for the purpose of casting crowns and other such dental restorations is similarly well known. Of particular note with regard to dental castings is the fact that dental castings require extreme accuracy in the final product. Accordingly, metallurgical characteristics have virtually dictated that the castings be prepared from precious metals such as gold and the like. Numerous attempts have been made to prepare dental castings from base metal alloys but heretofore base metal castings generally required excessive finish work so that the restoration will fit properly.
Yet another problem inherently present in all casting techniques utilizing the lost wax method is the fact that curing of the investment material is an exothermic reaction. In an exothermic reactions, the investment material generates heat as the investment material hardens or cures. This necessarily results in "swelling" of the investment material, and the swelling usually results in at least some compression of the wax model within the investment. The compression against the wax model for a dental restoration will have an undesirable effect of distorting the restoration pattern. When the pattern is burned out and a molten metal is cast into the void formed within the hardened investment material, the casting will not correspond exactly to the original pattern. This results not only in discomfort to the patient, but unnecessary expenditure of time, energy and money for the patient, the dentist, and the dental technician.
Insofar as the problem of obtaining accurate castings utilizing base metal alloys is concerned, the only effective solution available today involves either detailed and expensive hand-finishing of the casting, the taking of new impressions and making new castings, or simply accepting a relatively inferior final product. Another solution to this problem would be to prepare all castings from gold rather than a base metal alloy, but this obviously has an adverse economic impact on the patient.
U.S. Pat. No. 2,337,036 to Erdle discloses the use of a resilient mold for making porcelain dental restorations. While analogous to the field of preparing dental restorations, the resilient mold of U.S. Pat. No. 2,337,036 would not appear to be suitable for metal castings according to the lost wax process. U.S. Pat. No. 2,243,445 discloses an expansible absorbent receptacle for investments. U.S. Pat. No. 2,450,567 to Schwartz discloses a two-part flask for retaining investment material. Yet another casting ring constructed and arranged to prevent breakage of an investment made therein is disclosed in U.S. Pat. No. 1,976,655 to Carpenter.
While these patents disclose apparatus including investment ring constructions, none of these prior art teachings make any attempt to solve the problem created by the fact that as the exothermic reaction takes place before solidification of the investment material. As the wax pattern is subsequently burned out from within the investment material, different areas within the volume defined by the investment experience different temperatures.
In my prior invention filed as patent application Ser. No. 385,025 filed June 4, 1982, I disclosed an apparatus and a method for making improved full arch dental implants utilizing a unitary expandable investment ring in combination with a base and novel a sprue former and runner bar means. My prior invention as disclosed in application Ser. No. 385,025 solved many of the problems heretofore described and was issued U.S. Pat. No. 4,508,155.
In a further improvement upon my prior invention, I disclosed in application Ser. No. 718,178 filed Apr. 1, 1985 an improvement to the runner bar means which allowed even greater accuracy in full arch dental implants. The present application further improves upon the investment ring or container means set forth in my prior patent application Ser. Nos. 385,025 and 718,178.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention is a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.